1. Field of the Invention
The present invention relates to valves for a home solar heating apparatus, and in particular to valves both inhibiting thermosyphoning and indicating flow.
2. Description of the Prior Art
A solar heating apparatus for home use is well known and generally consists of a solar collector mounted on the roof, pipes connecting the solar collector with the hot water heater, and a circulating pump which circulates the water from the hot water heater through the solar collector and back. Usually, a thermostatic control for the circulating pump is provided so that when the temperature in the solar collector output drops below that of the hot water heater, the circulating pump is turned off because the solar collector has become, in effect, a radiator transferring heat from the water heater back to the atmosphere.
A problem with such a home solar heating apparatus is thermosyphoning which is the circulation caused by the density difference between hot and cold water and which may occur when the circulating pump is turned off. In short, if the water in the solar collector cools, such as at night, and the circulating pump is off, then the water at the collector supply (the lower inlet) is cooler and denser than the water at the collector return (the higher outlet). This difference in density forces the water in the supply line down into the water heater and the water in the return line up out of the heater and into the solar collector. Once in the solar collector, the warmer lighter water cools and becomes cooler denser water and flows down to the collector supply line, continuing the circulation. In order to prevent this thermosyphoning, electrical valves coupled with the circulating pump have been used, but such valves are expensive and subject to electrical component failure.
Another problem found in the usual home solar heating apparatus is the accumulation of air bubbles. The air bubbles will cause turbulence and lack of good thermal contact so that heat transfer efficiencies will drop at the solar collector and also will result in cavitation in the circulating pump and a consequent drop in the flow rate when the pump is on. Detection of such inefficiencies is difficult because the water flow is not visually observed, and when the circulating pump is turned on the homeowner presumes that the water is efficiently flowing to the solar collector to be efficiently heated.